Keep sub-second resolution when wrapping a DateTime value

Add `DateTime#usec` and `DateTime#nsec` so that `ActiveSupport::TimeWithZone`
keeps sub-second resolution when wrapping a `DateTime` value.

Fixes #10855

2 files changed, 11 insertions, 5 deletions

diff --git a/activesupport/lib/active_support/core_ext/date_time/conversions.rb b/activesupport/lib/active_support/core_ext/date_time/conversions.rb
index df07917d19..c44626aed9 100644
--- a/activesupport/lib/active_support/core_ext/date_time/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/date_time/conversions.rb
@@ -80,6 +80,16 @@ class DateTime
     seconds_since_unix_epoch.to_i
   end
 
+  # Returns the fraction of a second as microseconds
+  def usec
+    (sec_fraction * 1_000_000).to_i
+  end
+
+  # Returns the fraction of a second as nanoseconds
+  def nsec
+    (sec_fraction * 1_000_000_000).to_i
+  end
+
   private
 
   def offset_in_seconds
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index 4a032b0ad0..95b9b8e5ae 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -292,7 +292,7 @@ module ActiveSupport
       end
     end
 
-    %w(year mon month day mday wday yday hour min sec to_date).each do |method_name|
+    %w(year mon month day mday wday yday hour min sec usec nsec to_date).each do |method_name|
       class_eval <<-EOV, __FILE__, __LINE__ + 1
         def #{method_name}    # def month
           time.#{method_name} #   time.month
@@ -300,10 +300,6 @@ module ActiveSupport
       EOV
     end
 
-    def usec
-      time.respond_to?(:usec) ? time.usec : 0
-    end
-
     def to_a
       [time.sec, time.min, time.hour, time.day, time.mon, time.year, time.wday, time.yday, dst?, zone]
     end